The controlled experiment was carried out for the BBC Two documentary How safe are our Skies? Detroit Flight 253.

It would have been quite horrific - obviously the blast itself would cause eardrum rupture

Dr John Wyatt, international terrorism and explosives expert

Dr John Wyatt, an international terrorism and explosives adviser to the UN, replicated the conditions on board the Detroit flight on a decommissioned Boeing 747 at an aircraft graveyard in Gloucestershire, England.

The same amount of the explosive pentaerythritol (or PETN) allegedly carried by Mr Abdulmutallab was placed to mirror the location where he was sitting on the plane.

Captain J Joseph, an air accident investigator, and Dr Wyatt both concluded that the quantity of explosive used was nowhere near enough needed to rupture the skin of a passenger plane.

Dr Wyatt said: "If it was a more rigid material then we might have seen a crack or breakthrough but this is actually quite a flexible material.

"I was extremely impressed by the aircraft structure.

"It can sustain quite a hefty thump."

Captain Joseph said: "We noticed the aircraft had lost some rivets but no flight controls were compromised and certainly no fuel tanks were breached.

"I'm very confident that the flight crew could have taken this aeroplane without any incident at all and get it on the ground safely."

Body parts

However, the experts said that the death of the suspected bomber and the passenger sitting next to him would have been traumatic for passengers.

After seeing... how well the aircraft maintained its structural integrity, and obviously the pilot's capacity to fly the aircraft, it should give them (passengers) a great deal of confidence

Captain J Joseph, air accident investigator

"It would have been quite horrific. Obviously the blast itself would cause eardrum rupture," said Dr Wyatt.

Captain Joseph said the noise and the smoke would have been awful, "not to mention the parts of the bodies that were disintegrated as part of the explosion".

But Captain Joseph said the experiment could help to put air travellers at ease: "I think this should be a confidence-builder for passengers.

"After seeing... how well the aircraft maintained its structural integrity, and obviously the pilot's capacity to fly the aircraft, it should give them a great deal of confidence."

For security reasons, they could not go into specific details of blast damage inside the cabin of the test Boeing 747.

Kip Hawley, the former head of the US Transportation Security Administration (TSA) said: "We can be sure that al Qaeda and others have taken lessons from their failed attempt and this program allows the public to be privy to some of those lessons.

"An active and engaged public can not only be a layer of security but can be more effective in demanding the kind of security that will work.

"The explosives analysis done by Dr John Wyatt gave a realistic picture of the effects of a carry-on bomb roughly similar to the one used on Christmas Day.

FLIGHT 253

Umar Farouk Abdulmutallab, a Nigerian, is accused of trying to blow up the plane with a device hidden in his underwear

Officials say he planned to detonate it using a syringe filled with chemicals

Instead he caused a fire and was overpowered by passengers

He faces life imprisonment if convicted

Al-Qaeda in the Arabian Peninsula says it was responsible for the failed attack

"The point that today's airframes are more resilient than many imagine is a critical point.

"Governments do very sophisticated testing similar to what Dr Wyatt demonstrated and those results inform security measures you see in airports today.

"Specifically, it was that kind of testing that led to the decision to allow 100ml of any liquid, carried in a sealed one-quart baggie, to be brought through security."

Dr Wyatt's test results are to be shared with governments and aviation security experts around the world.

Some readers have questioned the validity of the experiment given that the plane was tested on the ground. The programme-makers gave this response:

At the time of the attempted detonation, Flight 253 was descending rapidly and its altitude has been estimated to be around 10,000ft.

At that height the difference in pressure inside and outside the plane would not have been great enough significantly to affect the explosion.

So the explosion team ruled that the decommissioned plane's lack of doors was not a factor in the test.

With this quantity of explosive, the peak pressure and impulse are over quickly and decay rapidly over distance. The doors were sufficiently far away that the overpressure would have dissipated before it reached them.

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